Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a plurality of base transceiver stations (BTSs) and a plurality of subscriber units, often termed mobile stations (MSs).
Wireless communication systems are distinguished over fixed communication systems, such as the public switched telephone network (PSTN), principally in that mobile stations move among BTS coverage areas, and in doing so encounter varying radio propagation environments.
In a wireless communication system, each BTS has associated with it a particular geographical coverage area (or cell). The coverage area is defined by a particular range where the BTS can maintain acceptable communications with MSs operating within its serving cell. Coverage areas for a plurality of BTSs can be aggregated for an extensive coverage area. An embodiment of the present invention is described with reference to the Third Generation Partnership Project (3 GPP) defining portions of the Universal Mobile Telecommunication Standard (UMTS), including the time division duplex (TDD) mode of operation. 3GPP standards and technical release relating to the present invention include: (i) 3GPP TS25.346 v6.0.0 “Introduction of Multimedia Broadcast Service (MBMS) in the Radio access Network: Stage 2;” (ii) 3GPP TR25.889 “Feasibility Study Considering the Viable Deployment of UTRA in Additional and Diverse Spectrum Arrangements;” (iii) 3GPP TR25.896 v6.0.0“Feasibility Study for Enhanced Uplink for UTRA FDD;” (iv) 3GPP TR25.848 v4.0.0 “Physical Layer Aspects of UTRA High Speed Downlink Packet Access;” (v) R1-050464 “Physical Channel Structures for Evolved UTRA” (NTT DoCoMo) RAN1 meeting number 41; and (vi) R1-050654 “Principles of E-UTRA Simulcast” (Qualcomm Europe) RAN1 LTE Adhoc meeting, all hereby incorporated within this application, in their entireties by reference. 3GPP documents can be obtained from 3GPP Support Office, 650 Route des Lucioles, Sophia Antipolis, Valbonne, FRANCE, or on the Internet at www.3gpp.org.
In UMTS terminology, a BTS is referred to as a Node B, and subscriber equipment (or mobile stations) are referred to as user equipment (UEs). With the rapid development of services provided to users in the wireless communication arena, UEs can encompass many forms of communication devices, from cellular phones or radios, through personal data accessories (PDAs) and MP-3 players to wireless video units and wireless internet units.
In UMTS terminology, the communication link from the Node B to a UE is referred to as the downlink channel. Conversely, the communication link from a UE to the Node B is referred to as the uplink channel.
In such wireless communication systems, methods for simultaneously using available communication resources exist where such communication resources are shared by a number of users (mobile stations). These methods are sometimes termed multiple access techniques. Typically, some communication resources (say communications channels, time-slots, code sequences, etc) are used for carrying traffic while other channels are used for transferring control information, such as call paging, between the Node Bs and the UEs.
It is worth noting that transport channels exist between the physical layer and the medium access control (MAC) in the system hierarchy. Transport channels can define how data is transferred over the radio interface. Logical channels exist between MAC and the radio link control (RLC)/radio resource control (RRC) layers. Logical channels define what is transported. Physical channels define what is actually sent over the radio interface, i.e. between layer 1 entities in a UE and a Node B.
A number of multiple access techniques exist, whereby a finite communication resource is divided according to attributes such as: (i) frequency division multiple access (FDMA) in which one of a plurality of channels at different frequencies is assigned to a particular mobile station for use during the duration of a call; (ii) time division multiple access (TDMA) whereby each communication resource, say a frequency channel used in the communication system, is shared among users by dividing the resource into a number of distinct time periods (time-slots, frames, etc.); and (iii) code division multiple access (CDMA) whereby communication is performed by using all of the respective frequencies, at all of the time periods, and the resource is shared by allocating each communication a particular code, to differentiate desired signals from undesired signals.
Within such multiple access techniques, different duplex (two-way communication) paths are arranged. Such paths can be arranged in a frequency division duplex (FDD) configuration, whereby a frequency is dedicated for uplink communication and a second frequency is dedicated for downlink communication. Alternatively, the paths can be arranged in a time division duplex (TDD) configuration, whereby a first time period is dedicated for uplink communication and a second time period is dedicated for downlink communication on an alternating basis.
Present day communication systems, both wireless and wire-line, have a requirement to transfer data between communications units. Data, in this context, includes signaling information and traffic such as data, video, and audio communication. Such data transfer needs to be effectively and efficiently provided for, in order to optimize the use of limited communication resources.
In a wireless telecommunications network, two broad classes of data transmission are supported: broadcast and unicast transmission. Broadcast transmissions are point to multipoint transmissions carrying downlink data targeted at groups of users whereas unicast transmissions are point to point links that typically carry bidirectional data between a single user and the network.
A user of telecommunication services accesses the services via a user equipment (UE) and those services are supplied by basestations (also referred to as Node Bs). The basestations may be connected to network elements deeper within the telecommunications network (such as the radio network controller: RNC). Hence broadcast services are provided from a basestation to multiple UEs via a downlink radio link whereas unicast services are provided from a basestation to a single UE via a bi-directional radio link.
Example broadcast services include: (i) news bulletins; (ii) weather reports; (iii) traffic reports; (iv) financial reports; (v) live (or near-live) sports highlights or video clips; and (vi) radio programming of pop or classical music—to name a few.
Example unicast services include voice calls and data calls (typically used for internet or business applications).
A network operator would typically require a user to subscribe to services that the user is interested in (and willing to pay for) and might provide security keys to that user in order to allow that user to decode and decrypt services that that user has subscribed to.
Wireless networks transmit data on radio waves. The range of frequencies over which these waves are transmitted is termed the radio spectrum. Conventionally, the radio communication link between a base station and a mobile station is termed a downlink or “DL.” The radio communication link between a mobile station and a base station is termed an uplink or “UL.” Radio spectrum may be paired in separate bands for uplink and downlink service, or it may be unpaired, in which a common band is time-shared between uplink and downlink service or the band is used solely for either uplink or downlink.
Paired spectrum consists of a downlink carrier and an uplink carrier (each covering a range of frequencies in the vicinity of the carrier). Bidirectional services are supported in paired spectrum by modulating uplink transmissions onto the uplink carrier and downlink transmissions onto the downlink carrier: this mode of operation is termed frequency division duplexing. The downlink and uplink carrier are typically separated by a guard band. An example allocation of paired spectrum is shown in FIG. 1a. In this example, the uplink portion of the paired allocation is within the frequency range 2550-2560 MHz and the downlink portion is within the frequency range 2670-2680 MHz. This paired allocation could be used by a single operator for the support of unicast or broadcast services (the broadcast services would be supported within the downlink portion of the paired allocation). Note that the figure shows bands within which paired allocations can be made (a regulator might allocate the specific paired allocations within the bands). Hence, although a paired allocation for a single operator is shown in FIG. 1a, in fact multiple paired allocations can be supported in the uplink and downlink bands.
Unpaired spectrum consists of a single allocation of spectrum. Unpaired spectrum can be used for the support of both unicast and broadcast services. In order to support bidirectional services, unpaired spectrum is switched between uplink and downlink modes (to create a time division duplex as opposed to the frequency division duplex that is typically used with paired spectrum). Broadcast services may be supported in unpaired spectrum by assigning some of the downlink time periods to broadcast services: indeed, all time periods in the unpaired spectrum may be assigned to broadcast services in which case the unpaired spectrum becomes a downlink-only, broadcast-only carrier. Unpaired spectrum could alternatively be used as an auxiliary downlink for another paired or unpaired carrier, though this aspect is not considered further in this disclosure. An example allocation of unpaired spectrum is shown in FIG. 1b. This figure shows an allocation of unpaired spectrum in the frequency range 2595 to 2605 MHz.
Wireless equipment that can receive and transmit at the same time typically has its transmitter and receiver operating at different frequencies; hence such equipment is referred to as a full duplex (FD) equipment. In time-related terms, a FD UE can transmit and receive at the same time as shown in FIG. 2 because UL and DL are in separate frequency bands. During time period A, two FD UEs (UE1 as white squares and UE2 as black squares indicating respective UL and DL periods of activity) are shown. Each UE can transmit and receive data at the same time. In time period B, only UE1 receives and there is no UL transmission from either UE (hence an FD mode UE has the ability to operate with downlink and uplink at the same time, but is not required to operate in such a fashion). In time period C, UE1 transmits in the uplink and there is a transmission to UE2 in the downlink. More sophisticated systems employing CDMA, Orthogonal Frequency Division Multiple Access (OFDM) or other advanced techniques allow multiple UEs to transmit and receive at the same time.
Wireless equipment that can receive and transmit at the same time needs to contain circuitry to ensure that transmissions do not interfere with receptions. This piece of circuitry is commonly referred to as a duplexer 0305 in FIG. 3. The relevant front end circuitry within an FD mode UE is shown in FIG. 3 (an FD mode UE can receive and transmit at the same time). The transmissions from the power amplifier 0303 in the UE shown in FIG. 3 are ideally strictly band limited (if the UE were operating in the paired allocation shown in FIG. 1, then the uplink transmissions would ideally be strictly band-limited to the range 2550-2560 MHz). In reality, it is not possible to produce a low cost, efficient power amplifier that is strictly band limited and there will inevitably be leakage of transmission power outside the nominal transmit frequency range. In order to produce a sensitive receiver (that can receive transmissions at a low power e.g. from a distant basestation, often referred to as a low noise amplifier or LNA), it is important that the power from the uplink transmissions does not leak into the receiver, hence the requirement for the duplexer. It is also important that the transmissions from the transmitter do not saturate the receiver. The duplexer 0305 acts to pass the transmit signal from the PA 0303 to the antenna 0306, but to attenuate the signal that passes between the PA 0303 and the LNA 0304 and ensures that the transmit signal from the PA 0303 does not saturate the LNA 0304.
The signals that are received by the UE may be of a low level (operation with low level signals is required when the UE operates at a great distance from the basestation as may be the case in a cellular wireless telephony system). The duplexer further acts to ensure that these low level received signals (at the receive frequencies, such as 2670-2680 MHz in the paired allocation shown in FIG. 1a) are passed to the receiver with little attenuation, ensuring that low level signals from distant basestations can be reliably received by the UE. Hence, at the receive frequencies, there is little attenuation between antenna 0306 and the LNA 0304.
The transmit and receive frequency characteristics in the UE are therefore of the form shown in FIG. 4a. This figure shows the transmit and receive characteristics for the example paired allocation of FIG. 1. The transmission is band limited (0503 the envelope marked “transmitter band limiting”), such that transmit power is constrained to the transmit portion of the spectrum (to the extent possible within cost and power constraints) and the reception is band limited (0504 the envelope marked “receiver band limiting”), such that power is constrained to be received within the receive portion of the spectrum (again to the extent possible within cost and power constraints).
Operation of the front end circuitry in the basestation is conceptually similar to operation of the front end circuitry in the UE, but the basestation transmits in the downlink and receives in the uplink. The front end architecture in the basestation is thus similar to that shown in FIG. 3. The basestation is a fixed piece of equipment that is owned by a network operator (as opposed to the UE which is a mobile piece of equipment that is typically paid for by the subscriber—in one way or another). It is thus possible to implement higher cost and higher power components in the basestation (since there are fewer basestations, these base stations are mains powered and owned by corporations). Hence it is feasible to filter transmissions and receptions more aggressively in the basestation (using higher precision, though higher cost and higher power components). Hence the transmit and receive characteristics of a basestation may be superior (in a spectral sense) to those of the UE. The transmit and receive characteristics of the basestation may thus be as shown in FIG. 4b. 
Half duplex mode operation can occur in paired or unpaired spectrum. For half duplex mode operation in paired spectrum UL transmissions occur on one frequency, DL transmissions occur on a different frequency. At the UE, the transmitter and receiver never operate together at the same time; at the basestation, the UE transmitter and receiver can operate together at the same time (i.e. the UE can operate in strict half-duplex mode and the basestation can operate in full-duplex mode). For half duplex mode in unpaired spectrum UL and DL transmissions occur on one (and the same) frequency. UL and DL transmissions are separate in time (via time division multiplexing). This mode of operation is typically referred to as time division duplex (TDD) operation.
FIG. 5 shows the time and frequency related aspects of half duplex mode operation in paired spectrum. During time period A, UE1 (white squares denoting activity) and UE2 (black squares denoting activity) operate bidirectional services. The basestation ensures that UE1 never needs to transmit and receive at the same time (hence it staggers the times at which UE1 has to transmit and receive). Similarly, UE2 is never required to transmit and receive at the same time. Note that by scheduling transmissions to UE1 and UE2 appropriately, all of the uplink and downlink resource can be used. During time period B, a unidirectional downlink service is applied to UE1. During time period C, a unidirectional uplink service is applied to UE1. Note that while this UE is being supplied with uplink service, downlink allocations to UE2 are possible. Note how in the figure shown the UE operates strictly in a half-duplex fashion, but the basestation operates in a full duplex fashion. Note again that for the sake of simplicity, a basic half-duplex scheme is shown, but in more advanced half-duplex transmission schemes (employing CDMA or OFDM technology), it is possible to serve multiple UEs at any one time: the rules remain the same however—an uplink transmission to a UE can never coincide with a downlink transmission to a UE.
FIG. 6 shows the time and frequency related aspects of half duplex mode operation in unpaired spectrum. In time periods A and B, bidirectional services are supported. UE1 and UE2 activity is denoted by white and hatched squares, respectively. The uplink portions of the bidirectional service are transmitted during time period A and the downlink portions of the bidirectional service are transmitted during time period B, as indicated by up and down arrows, respectively. In time period C, an uplink unidirectional service is applied to UE1. In time period D, a downlink unidirectional service is applied to UE1.
Note that a certain switching order between uplink and downlink is shown in FIG. 6, but this should not be considered to be prescriptive and in reality there are many different switching orders between downlink and uplink transmissions that can be applied. Note also that as for the FD and half-duplex mode in paired spectrum operation cases, only a simple system is shown where only a single UE transmits or receives at a single time instant, but in general multiple UEs can transmit in an uplink timeslot or multiple UEs can receive in a downlink timeslot when advanced techniques such as OFDM or CDMA are applied.
The UE architecture for a half duplex mode UE is simpler than that for a full duplex mode UE. A simplified diagram showing UE architecture is illustrated in FIG. 7. The half-duplex UE front-end architecture is considered to be simpler than the FDD UE front-end architecture as it does not contain a duplexer. Instead of the duplexer, the half-duplex UE contains a switch 0701 and transmit 0702 and receive 0703 bandpass filters. Note that in this architecture (and by virtue of the rules by which half-duplex UEs operate), there is no way for the UE's uplink transmissions to interfere with the UE's downlink receptions. The UE architecture of FIG. 7 may be used for either paired operation or unpaired operation.
The front-end architecture of a basestation operating in paired spectrum, serving half-duplex UEs, can be the same as that of the full-duplex basestation as shown in FIG. 3.
The front-end architecture of the basestation operating in unpaired spectrum can be similar to that of the UE shown in FIG. 7.
The frequency characteristics of the UE and basestation when operating in paired spectrum are shown in FIGS. 8a through 8c. FIG. 8a shows the basestation operating in full-duplex mode and FIGS. 8b and 8c show the UE operating in a strictly half-duplex fashion. As for the full duplex case, the basestation receiver and transmitter band limiting may be reasonably tight (due to the possibility to use higher precision and costlier components in the basestation than in the UE). FIGS. 8b and 8c illustrate UL and DL receiver characteristics of a UE, respectively. These are shown separately as the UE transmitter can never interfere with the UE receiver when operated in half-duplex mode (due to uplink and downlink transmissions always being separated in time).
The frequency characteristics of a UE operating in unpaired spectrum is shown in FIGS. 9a and 9b, respectively. The frequency characteristics of a basestation when operating in unpaired spectrum is shown in FIGS. 10a and 10b, respectively. This figure shows the basestation and the UE operating in half-duplex mode. It is possible neither in the basestation nor in the UE for the uplink transmissions to interfere with the downlink transmissions due to the orthogonality of these transmissions in the time domain.
3GPP has standardized the use of downlink resources for the transmission and reception of broadcast and multicast services. This system is referred to as the Multimedia Broadcast Multicast Service (MBMS). In this system, the broadcast traffic is either time multiplexed, code multiplexed, or time and code multiplexed with other traffic onto an existing carrier. In 3GPP, it has also been proposed to use unpaired spectrum as a standalone carrier for downlink MBMS data.
Unpaired spectrum is highly useful when operated as a standalone carrier carrying unicast data (such as internet and voice traffic). It is however also highly desirable to be able to use unpaired spectrum for the provision of downlink only broadcast services. When unpaired spectrum is used for a broadcast service it is typically paired in some loose sense with a bidirectional carrier. The bidirectional carrier may be used for signaling security information to allow the broadcast services to be decrypted and received or may be used to carry internet or voice traffic at the same time as the broadcast services (there are many possible other scenarios in which a bidirectional carrier and broadcast carrier may be used at the same time).
There are broadly two possible cases for the spectrum occupied by the downlink broadcast carrier: the broadcast carrier can occupy frequencies that are greater than those for the unicast downlink carrier (outside the duplex) or it can occupy frequencies between the unicast downlink carrier and the unicast uplink carrier (inside the duplex).
The case where the broadcast downlink carrier is outside the duplex spacing is shown in FIGS. 11a and b, for a basestation and UE, respectively. In this case, the broadcast downlink carrier is sufficiently separated from the uplink carrier that there is insignificant interference between the uplink carrier and the broadcast downlink carrier in the UE or basestation. Hence it is directly feasible to operate a broadcast downlink carrier outside the duplex of the paired unicast carrier with little additional complexity (the duplexer may need to have a wider passband for reception of both the unicast and downlink broadcast carriers).
Spectrum is a scarce resource and it is not always possible to ensure that the MBMS auxiliary downlink carrier is outside the duplex for the unicast carrier. For example it would be highly desirable to be able to use the unpaired spectrum allocation shown in FIG. 1b as an auxiliary MBMS downlink carrier is conjunction with a paired spectrum allocation such as that shown in FIG. 1a. However, use of unpaired spectrum as an auxiliary downlink broadcast carrier inside the duplex is much more problematic than the case where the auxiliary downlink broadcast carrier is outside the duplex. This issue is illustrated in FIGS. 12 and 13. FIG. 12 illustrates base station frequency characteristics. The transmit and receive filters for a base station can have tight specifications because of a relative lack of cost, size, and power constraints, compared with mobile stations. FIG. 13a illustrates transmit and receive filter characteristics having tight specifications for a mobile station, that has a high cost and power consumption. FIG. 13b illustrates more practical transmit and receive filter characteristics, showing excessive interference in the UE DL from the UE UL.
In order to reduce interference between uplink transmissions (of unicast data) and downlink broadcast transmissions, one approach is to tighten the requirements on the UE duplexer 0305 as shown in FIG. 3. The duplexer would need to reduce the range of frequencies that uplink transmissions spuriously create and would need to be more selective in terms of the frequencies that are allowed for reception (i.e. the UE receive filter would need to have a sharper roll-off). These tighter duplexer requirements lead to a higher cost, higher power consumption UE (higher precision components are typically more expensive and use more power). The frequency characteristics of this high cost, higher power consumption UE are shown in FIG. 13a. 
A lower cost, lower power UE design would suffer from excessive interference into its downlink receiver whenever the UE uplink is used due to spurious emissions from the UE uplink not being sufficiently attenuated by the UE duplexer (note that the transmitter and receiver band limiting is not as tight for the low cost, low power UE shown in FIG. 13b—in comparison to the higher cost, higher power UEs shown in the FIG. 13a). This excessive interference will either increase the power required to supply downlink services to the UE (both broadcast and the downlink part of unicast services) or will reduce the coverage area of downlink services (both unicast and broadcast).
There is hence a need to be able to operate downlink broadcast services inside the duplex of a unicast carrier in a low cost and power efficient manner. The current invention provides a solution that meets this need.
Time multiplexing aspects of MBMS/E-MBMS (note E-MBMS is a term for enhanced MBMS: E-MBMS still supports multicast and broadcast services) with other services are shown in FIG. 14 (this is taken from R1-050654 “Principles of E-UTRA simulcast,” incorporated by reference, above). This FIG. 14 shows that for an auxiliary downlink (on carrier f1), MBMS services are transmitted continuously (but there can be multiplexing between different services at different times). The figure also shows that a carrier can be time multiplexed between supporting MBMS and supporting unicast data (carrier f3). Note that in this figure, carriers f2, f3 and f4 are at the duplex spacing and carrier f1 is outside the duplex spacing.
Both broadcast data transmissions and unicast transmissions are scheduled to an extent in the background art. In MBMS (a 3GPP scheme for the transmission of broadcast data), the broadcast data (on the MBMS traffic channel—MTCH) can be scheduled. When MBMS data is scheduled, the network decides at which times various different MBMS services are going to be transmitted on different cells: this information is then signaled to UEs via an MBMS scheduling channel (MSCH). A UE may use the scheduling information carried on MSCH to reconfigure its receiver to receive MBMS transmissions from particular cells at particular time instants (if an MBMS transmission is transmitted at the same time from more than one cell, then the UE may find it advantageous to receive and combine the transmissions from these multiple cells). Scheduling of MBMS transmissions is described in 3GPP TS25.346 v6.0.0 “Introduction of the Multimedia Broadcast Multicast Service (MBMS) in the Radio Access Network (RAN); Stage 2,” incorporated by reference, above. Note that in the background art, MBMS transmissions are not scheduled on the basis of MBMS services that UEs are decoding.
In 3GPP, both uplink and downlink unicast data may be scheduled. Unicast data is typically scheduled for packet based services (carrying for example internet traffic) and is not scheduled for circuit switched services (carrying for example voice traffic. Note: there may be a degree of scheduling for circuit switched services when call admission control (CAC) and dynamic channel allocation (DCA) techniques are considered). Aspects of scheduling for uplink and downlink unicast services are described in 3GPP TR25.896 v6.0.0 “Feasibility Study for Enhanced Uplink for UTRA FDD” and 3GPP TR25.848 v4.0.0 “Physical layer aspects of UTRA High Speed Downlink Packet Access,” both incorporated by reference, above. These documents cover high speed uplink packet access and high speed downlink packet access (together termed high speed packet access: HSPA).
In HSPA, UEs are scheduled by the basestation according to parameters such as: (i) channel conditions; (ii) buffer volume (availability of data to transmit); (iii) estimated interference created in own and neighbor cells (this technique is especially applicable to high speed uplink packet access); (iv) fairness criteria; (v) quality of service attributes; and (vi) others.